The Social Security Death Index, which is sometimes abbreviated as the SSDI, is a database which includes death records for holders of Social Security numbers. The information in the index is available online, at no charge. The database has been compiled by the Social Security Administration, using information from the reports made to the agency following the deaths of people who have been issued a Social Security number.

When someone who holds a Social Security number dies, their death will be reported to the Social Security Administration. The Social Security Administration records deaths in its Death Master File. The SSDI is an extract of this file. Members of the public cannot access the Death Master File itself, but they can easily access the information in the Index. The Social Security Administration is required to make this information public because they are a government agency. The Death Master File is used by the Administration to prevent fraud by providing a means of checking that the Social Security number of a deceased person is not being used by anyone.

Since most people working in modern America will require a Social Security number, most of the people who have died in the United States since the year 1962 have been holders of Social Security numbers. The Social Security system was first created in 1935. Most people who have worked in the United States since this time have used a Social Security number in order to pay taxes and receive retirement and other forms of Social Security benefits.

The Social Security Death Index now contains records for more than 84 million people. It has been estimated that between 93 and 96 percent of the people over the age of 65 who die in the US have been recorded in the Index since the year 1972.

Each entry in the SSDI includes a selection of information about the individual whose death has been recorded. This includes the person's given name and surname, as well as their middle initial in some cases. The entry also includes the individual's date of birth and either the date of their death or, if the account has not been active from the year 2000 onwards, the month and year of their death. The individual's Social Security number and the territory or state in which this number was issued is also provided, as is the last known place of residence of the deceased.

It is also possible to obtain more information about an individual who has been listed in the SSDI, by ordering from the Social Security Administration a copy of the individual's original application for a Social Security number. This form, which is known as the SS-5 form, contains additional details about the individuals, notably the location in which they were born, their father's name and their mother's maiden name. This can be particularly helpful for genealogical research.

The Social Security Death Index has proved a useful resource for genealogists and individuals researching their family history. The information that it contains can be useful for genealogy, historical research and biographical writing, particularly since it is available online for free. Despite being a useful tool, the SSDI has been involved in some controversy, due to the problems caused when people have been incorrectly listed in the index, when it has proven very difficult for them to convince the Administration that they are actually still alive. An audit revealed that there were 23,000 incorrect listings within a single two year period.